In a typical prior art magnetic disk recording system a slider containing magnetic transducers for reading and writing magnetic transitions flies above the disk while it is being rotated by a spindle motor. The disk includes a plurality of thin films and at least one ferromagnetic thin film in which the recording (write) head records the magnetic transitions in which information is encoded. The magnetic domains in the media on can be written longitudinally or perpendicularly. The read and write head portions of the slider are built-up in layers using thin film processing techniques. Typically the read head is formed first, but the write head can also be fabricated first. The conventional write head is inductive.
In a disk drive using perpendicular recording the recording head is designed to direct magnetic flux through the recording layer in a direction which is generally perpendicular to the plane of the disk. Typically the disk for perpendicular recording has a hard magnetic recording layer and a magnetically soft underlayer. During recording operations using a single-pole type head, magnetic flux is directed from the main pole of the recording head perpendicularly through the hard magnetic recording layer, then into the plane of the soft underlayer and back to the return pole in the recording head. The shape and size of the main pole and any shields are the primary factors in determining the track width.
FIG. 1 illustrates a prior art head 26 for perpendicular recording and the associated media 27 in a disk drive 20. The section is taken perpendicular to the ABS. This figure and the others included herein are not to scale, in part, because the smaller components and spacings would be unclear. Places where the relative sizes and dimensions are significant will be noted if not known to those skilled in the art. The ABS is shown without a thin film protective overcoat which would normally be present in a production head. The term ABS as used herein means the plane as shown in the drawings without regard to whether an overcoat is present. The read sensor and its shields are not shown in FIG. 1, but could be located either to the left or right side of the write head. This design has a single coil 35. The yoke is composed of ferromagnetic pole pieces 41, 42, 43, 45 and 46. The floating trailing shield 44 is not part of the yoke. The movement of the magnetic recording medium is from the main pole piece or write pole 42 to the trailing shield 44, hence the label “trailing.” The stitch pole piece 41 provides the needed mass of ferromagnetic material for the main pole piece 42, but does not extend to the ABS. Only the small area of the main pole 42 appears at the ABS. The back of the yoke 46 (often called the “back gap” for historical reasons) directly connects the stitch pole piece 41 to the return pole piece 43. The trailing shield 44 has a simple rectangular cross-section in this design, but other shapes are possible. The conventional method for producing a head as shown in FIG. 1 is to form the structures starting with the return pole piece 43 on the right. The ABS is exposed when the wafer is cut after the structures have been formed. FIG. 2 illustrates a wafer 25 on which a plurality of write heads are being fabricated. The full film trailing shield gap layer 47 has been deposited on completed main pole piece 42. A photoresist 49 has been patterned with a void which will be used to form the trailing shield in subsequent steps. The right hand edge of the photoresist 49 determines the final back edge of the trailing shield. The dimension of the trailing shield measured perpendicular from the ABS into the head is known as the “throat.” The term trailing shield thickness is used to mean the dimension of the trailing shield along the ABS from the trailing shield gap layer 47 to the left edge as shown in FIG. 1. The cut for the ABS (and any lapping) determines the final ABS plane of the trailing shield. The use of a conventional photoresist for determining the throat of the trailing shield leads to imprecision which is unacceptable as the dimensions of write head designs shrink. The photoresist material is subject to erosion by the processes which are used to deposit the ferromagnetic material for the trailing shield which include plasma ashing and acid dipping as preparatory steps for electroplating NiFe. The photoresist for the electroplating process must be relatively thick which limits the achievable aspect ratio (thickness:throat ratio) for the trailing shield. Future write heads require a higher aspect ratio for the trailing shield than the current photoresist technique provides.